Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$240.72	5.665%	$254.3568	$254.36	$254.35	$254.40
Purchase #2	$176.74	4.684%	$185.0185	$185.02	$185.00	$185.00
Purchase #3	$130.35	13.846%	$148.3983	$148.40	$148.40	$148.40
Purchase #4	$120.27	12.739%	$135.5912	$135.59	$135.60	$135.60
Purchase #5	$53.83	10.654%	$59.565	$59.57	$59.55	$59.60
Purchase #6	$82.47	7.570%	$88.713	$88.71	$88.70	$88.70
Purchase #7	$97.81	6.486%	$104.154	$104.15	$104.15	$104.20
7 purchase totals =	$902.19		$975.7968	$975.80	$975.75	$975.90